Five men are on the ballot for New York City mayor in the Sept. 12 Democratic primary. (In writing this, we first checked the calendar to make sure it was 2017. Not a single woman, or for that matter, a single nonwhite candidate, is in the race for the party’s nomination.) Of the five, only two took part in a televised debate at a Manhattan theater Wednesday evening: Mayor Bill de Blasio and his presumed main opponent, Sal Albanese. The others had not raised enough money to qualify to be on that stage.

The debate sponsors, led by NY1, followed a qualifying standard set by the city’s Campaign Finance Board for disbursing matching campaign funds. Candidates had to raise and spend at least $175,000. That was chump change for Mr. de Blasio. Mr. Albanese, a former city councilman who has not held public office for two decades, crossed the threshold with barely a buck to spare.

There is logic in setting a dollar minimum to show that a candidate has a detectable political pulse. But it puts a price tag on the democratic process, particularly troubling in a city where affordability is a dominant concern. “Thresholds deprive the voters of choices,” said Jerry Goldfeder, a New York election lawyer. As for defining a candidate’s seriousness, he said, “the electorate loves to surprise pundits.”

Since Mr. de Blasio’s other challengers collected enough signatures on nominating petitions to qualify to run, why exclude them from a debate, whether the one on Wednesday or a follow-up set for Sept. 6? Granted, relying solely on signatures could foster a come-one come-all spirit, with debates then including oddballs whose entertainment value far exceeds their political viability. That’s been known to happen. It would probably also lead to well-heeled candidates challenging every jot and tittle of their poorer rivals’ petitions — a familiar, unsavory practice in New York.

Nonetheless, the three excluded Democrats could have added depth to the debate. Robert Gangi, for instance, has long been a gadfly advocating criminal justice reform. He would have, for sure, provocatively challenged both Mr. de Blasio and Mr. Albanese on “broken windows” policing and its impact on predominantly black and Latino neighborhoods. That issue got no attention.

This has been an uninspired mayoral race. None of the mayor’s opponents qualify as household names — not Richard Bashner, a community board member in Brooklyn; not Michael Tolkin, a technology entrepreneur; not Mr. Gangi; not even Mr. Albanese, though he has run for mayor twice before. The last time, in 2013, he got less than 1 percent of the vote in a crowded Democratic primary.

Voter-approved limits that confine city officeholders to two four-year terms might also have had an unfortunate effect. Better-known Democrats who already hold elective office and could have been stronger competitors apparently decided to wait Mr. de Blasio out. Assuming Mr. de Blasio wins re-election, he must leave City Hall at the end of 2021. Some political scientists are convinced that without term limits, and denied the option of avoiding an incumbent, a few of those officials — like Representative Hakeem Jeffries of Brooklyn and Queens or the city comptroller, Scott Stringer — might have been tempted to take on the mayor now.

Given the weak field, more inclusive debates could give challengers a better chance. Early in the 2013 election cycle, debates helped lift a mayoral contender who barely cracked 10 percent in polls. His name was Bill de Blasio.